An electronic sewing machine equipped with a needle threading device has conventionally been used to form stitches on a workpiece cloth. Such a needle threading device of the sewing machine is capable of threading a sewing needle with ease by manually operating a needle threading lever after hooking an upper thread drawn from a thread spool onto a thread tension regulator, a thread take-up, and the like.
For example, a needle threading device of a sewing machine disclosed in Japanese Patent No. 2002-200387 is provided with a needle threading shaft and a slider guide shaft supported vertically movably by a needle bar base that supports a needle bar and a hook retaining member fixed to a lower end of a needle threading shaft. The aforementioned needle threading device is further provided with a hook mechanism fixed to the hook retaining member, a first thread guide member fixed to the hook retaining member and a second thread guide member which is substantially C-shaped in side view and is rotatably supported by the lower end of the needle threading shaft, and the like. Furthermore, in the above described needle threading device, the upper thread drawn from the thread spool is hooked onto predetermined thread hooking portions then to the needle bar thread guide and onto the first and the second thread guide members. After retaining the upper thread by thread guide discs (thread retaining member) provided on the lower end of the needle threading shaft and the slider guide shaft, the upper thread is cut by the thread cutter provided on a sewing machine head.
In such construction, when the needle threading operation lever is lowered, the needle threading shaft is rotated after the needle threading shaft and the slider guide shaft are lowered to the predetermined position. By the rotation of the needle threading shaft, the first and the second thread guide members rotate in the direction moving away from each other and cooperatively retain the upper thread in a predetermined location near the needle eye of the sewing needle while the needle threading hook also rotates so as to pass through the needle eye of the sewing needle and hooks the upper thread. Then, when the needle threading operation lever is released, the needle threading hook is rotated in the reverting direction and pulled out of the needle eye with the upper thread hooked. Then, the needle threading shaft and the slider guide shaft are raised simultaneously, and the needle threading is completed.
In the needle threading device of a sewing machine disclosed in Japanese Patent No. 2002-200387, the upper thread is hooked by the needle threading hook and pulled back in the rear of the needle eye. However, the thread end of the upper thread remains in the front side of the needle eye without being pulled out therefrom; consequently forming an upper thread loop in the rear of the needle eye and the needle threading operation is terminated in such state. Therefore, the user is required to pull out the upper thread end from the needle eye by pulling the upper thread loop reward with his/her fingers, which complicates and interrupts the needle threading work.
As described above, the reason for not being able to pull out the thread end of the upper thread from the needle eye of the sewing needle is that the length of the thread end required for needle threading cannot be shortened. The reason for not being able to shorten the length of the thread end is that the distance of the vertical movement of the needle threading hook from a stand-by position, in which the thread is hooked, to a needle threading position, in which the needle threading hook is rotated after being lowered, is small. Another reason is that a thread retaining member that retains the thread end of the upper thread and a thread cutter that cuts the upper thread are distanced from the needle eye of the sewing needle, thereby being unable to shorten the length of the thread end required for needle threading.
In such case, in order to resolve the first reason, the vertical movement of the needle threading hook can be increased to a possible extent so as to reliably pull out the thread end from the needle eye by the reverting movement of the needle threading hook. However, in a household electronic sewing machine where size reduction is a critical demand, a plurality of mechanisms such as a needle bar vertically moving mechanism, a needle bar swinging mechanism, presser foot vertically moving mechanism are arranged in a compact manner in the sewing machine head; hence, it is difficult to secure enough vertical space. Thus, it is not possible to increase the vertical movement range of the needle threading hook.
Also, to resolve the second reason of being unable to shorten the length of the thread end required for threading because of the distanced arrangement of the thread retaining member that holds the thread end and the thread cutter that cuts the upper thread from the needle eye of the sewing needle, the following can be conceived. The thread retaining member and the thread cutter can be disposed close to the sewing needle. This is aimed to shorten the length of the thread end and to allow the thread end to be reliably pulled out by the reverting movement of the needle threading hook. However, since the thread retaining member is arranged to be provided in the lower stream in the thread supplying direction than the second thread guide member, the thread retaining member is compelled to be placed in a remote location, therefore, the thread end length cannot be shortened.
Furthermore, since the thread end length for needle threading, that is, the thread end length at the time of sewing start is long, after completion of sewing, the thread end extending from the workpiece cloth in the sewing start position need to be cut off, leading to a waste of sewing thread.